Evolution of fiber distributions in homogenized constrained mixture models of soft tissue growth and remodeling: Uniaxial loading

Growth and remodeling in soft tissue changes, in general, the orientation distribution of the collagen fibers in the tissue. So far, the governing principles are still incompletely understood. In this paper, we derive from the homogenized constrained mixture theory of soft tissue growth and remodeling - under some simplifying assumptions - a theoretical framework that enables simple analytical solutions that help to understand the evolution of the collagen fiber distribution in soft tissues during growth and remodeling under uniaxial loading. Our analysis suggests a natural tendency of the collagen fiber distribution to form a peak in the direction of loading and a spread increasing with the ratio of the fiber half-life time and the time constant governing loading-related fiber production. This observation helps to understand why in vivo collagen fiber reinforcement is typically organized in the form of (often von Mises-like) distributions with a finite spread. Our analysis also suggests a considerable history dependence of the fiber distribution evolution, which may explain why, in tissues under the same type of loading, sometimes considerably different fiber orientation distributions are observed.